Vanity Light - No receptical?

I'm in the process of refinishing a power room. The light above the vanity was one of those light bars with 4 bulbs. My wife hated that light so I took it down to replace it with a new one. Here's my problem...

There is no wiring box behind the light (just a hole in the wall with the wires pulled through). Now, I'm looking to install a new sconce-type light and I know they tyically will attach to the wall via screws that go through the corners of the junction box. My wall doesn't have one of these junction boxes and I can't install one, because dead-center in this wall (where is where I want to install the light) there is a pvc drain pipe from an upstairs bathroom. Any thoughts on how I'll be able to install the new sconce without having to install a junction box? Any advice would be great!

You will have to go with two lights (one on either side of the drain pipe), or a light similar to what was there previously (a surface mount light with an integral junction box), or you will have to move the drain pipe.

there are flat boxes avaliable that can serve as the 'box'. they are 4" round and have no weight rating. all they are is a way to junction in the canopy of the light in a situation that you can not mount or there was no box. never used them, but i have seen them. I dont like mounting to the rock alone, even with an oldwork box. when the rock absorbs moisture it becomes brittle and the light can fall.

I've got an almost identical situation, so I'll throw it in here. I had one of those 4 light incandescent fixtures that was old, so I bought one just like it. It turns out that my ceiling box is there, but it is off center. They (wrongly) had the wires coming out of the fixture and over to the left and into the box. The drywall behind the old fixture in the center (where the box should have been) was actually darkened. The directions for the fixture say it must be mounted on a box (in the center.) I can't easily move the box over to center because there is no stud there, plus there are a lot of wires going through here. I was considering either building a wooden frame above the mirror and putting a box in it and mounting the fixture to that, or taking it back and finding a fixture that can have Romex going straight into the fixture and terminating there, but I'm not sure how many of those I'll find.